ZURICH—Building-materials company LafargeHolcim Ltd. posted a first-quarter net loss Thursday on weaker-than-expected sales, but said it remains on track to deliver its longer-term targets amid “challenging economic headwinds” in emerging markets.

The company, based in Jona, Switzerland, said it made a net loss of 47 million Swiss francs ($48.38 million) for the first quarter, which was a 22 million franc improvement on the same quarter of 2015 after the exclusion of divestment gains. Net sales were 6.06 billion francs, down...